Skin surface nanoscale topography by light interferometry
Résumé
The skin is the first thing one perceives of a person. Unconsciously, its color, its radiance and its complexion give us a first impression of a person. This is why cosmetic care and makeup products are of great importance.
But how to evaluate their activity?
Many methods of in vivo measurements exist to evaluate its color or shine, but the evaluation of a product activity on skin surface is much more complicated.. The relief of the skin and even more its microrelief, are largely responsible for its optical properties and therefore the image it refers.
Many products have a filling or a tensor effect, modifying the depth and width of the microfolds that compose the microrelief. It is consequently necessary to measure and characterize the skin surface before and after the application of a cosmetic product with great precision.
More precise than 3D scanners, or the fringe projections in vivo, light interferometry allows making a topographical survey of the skin surface with an accuracy of a few tens of nanometers.
The topography by light interferometry is developed by the Polytec company whose experience in measuring equipment is no longer to be proved.
This technology used in particular in the control of mechanical parts of aeronautics, offers a lateral resolution of approximately 10 μm and a vertical resolution of less than 20 nm.
Depending on the light interference reflected from the surface of the skin, this technology is sensitive to vibrations which avoids its in vivo use.
To benefit from this technology usually reserved for the world of precision micromechanics, we have developed a support to put under tension a human living skin explant and to maintain it in survival ex vivo.
This support specially designed and printed in 3D allows stretching the skin on a reservoir of culture medium while respecting a tension similar to the in vivo conditions.
The tension of the skin was measured and verified by cutometry. This measurement can also be performed during the study which can last up to 10 days.
The skin thus stretched can be topographed and treated by different products. So it will be very simple to measure the roughness of the surface of the skin, the depth of its folds or their width.
We applied on the surface of the skin three products, two with smoothing and filling activity. We showed a decrease in the average depth of the cutaneous microfolds as well as a decrease of the roughness of the skin.
If an immediate effect can be observed in a few minutes, the ex vivo character of this model also allows evaluating a biological activity which reinforces in depth this surface-visible effect.
This new and original approach, coupling light interferometry technology and human living skin explant, offers all the precision and finesse necessary for an immediate evaluation of the activity of a product on skin surface proprieties and to investigate in parallel the cutaneous-linked biological effects.